1. Field of the Invention
The present invention relates to a throttle valve control apparatus for an internal combustion engine mounted on a vehicle.
2. Description of Background Information
As an example of throttle valve control apparatus, there is a known arrangement in which an operation position of a throttle valve is detected and the throttle valve is driven according to an opening characteristic which is previously determined correspondingly to the detected operation position, such as an apparatus disclosed in Japanese patent application laid open No. P 60-164630.
On the other hand, there have been continuous studies on the control of throttle valve opening in order to minimize the fuel consumption of an internal combustion engine. For example, an apparatus is proposed by the present applicant, in which a target opening of a throttle valve at which the minimum fuel consumption rate (BSFC) is obtained is established in connection with the rotational speed of the engine, and the throttle valve is driven by means of a motor for example in a manner to reduce the deviation of an actual throttle valve opening from the target throttle valve opening. However, with such a throttle valve control operation, the output power of the engine may become insufficient in a power requiring range of engine operation such as an accelerating state in which the generation of high engine output power is preferable to the fuel economy, thus deteriorating the driveability of the engine. Moreover, if the apparatus is designed to switch the control mode of the throttle valve upon transition of the engine operation from an economical driving requiring range to the power requiring range, a rapid increase of the throttle valve opening may occur, to generate a shock. Thus, a smooth transition of the engine operation may not be possible.